This invention pertains to rotary valve actuators primarily utilized to provide remote operation for fluid control valves. Powered valve operation is further required for very large valves such as used in water supply or sewage treatment systems where manual operation is inconvenient and/or too slow for the system requirements.
Recent valve applications brought about by heightened interest in conservation of natural resources such as atmospheric air and the earth's bodies of water have dictated stringent reliability requirements. In particular, the capability of returning to a safe or predetermined closure condition is of great importance in modern valve actuator design.
Valve designs currently known and utilized are exemplified by U.S. Pat. Nos. 3,808,895, 3,430,916, and 3,279,744. The units disclosed all provide fail safe return to one position, that is full open or full closed, or the other. While this characteristic satisfies certain of the above mentioned requirements, there is need for a valve actuator which provides the fail safe return along with capability of continuous positioning of the valve shaft, or modulation of the valve output. An additional shortcoming of the above mentioned prior art valves is the requirement that the valve drive unit furnish sufficient torque to energize the storage unit and overcome the inherent valve operating resistance simultaneously. This characteristic places a substantially larger burden on the drive system and results in much larger drive hardware and/or reduced life of the drive components such as electric motors, hydraulic cylinders, or pneumatic cylinders. A further shortcoming of the above valves lies in the method of release provided for the stored energy component. In each case, mechanical devices such as rapid rise cams or seer mechanisms are utilized to provide release of the storage unit. Unfortunately, these components inherently result in high pressure metal contact with resultant rapid wear and short life or inaccurate release positions.
In view of the above, the invention disclosed here provides a fail safe valve actuator capable of continuously positioning the valve shaft and at the same time requiring only the force required to charge the storage systems or operate the valve. Therefore, it is not necessary to oversize the drive motor to provide adequate torque. In addition, the invention disclosed utilizes relative simple and wear resistant devices to contain the forces of the stored energy capsule, resulting in improved reliability of the overall unit.